Observations on the distribution and the time sequences of calcium accumulation following single and repetitive ischemic insults using 45calcium autoradiography revealed significant differences in the pattern of calcium uptake between single and repeated occlusions. A striking feature of calcium accumulation in repeated ischemia was intense uptake of Ca + + in thalamus, striatum and, later, in the medial geniculate and substantia nigra. Also, a striking finding was an intense Ca + + uptake in CAl when the pyramidal neurons were virtually destroyed. Our observations suggest that abnormal accumulation of calcium may be due to other causes than a direct ischemic injury and may not necessarily indicate irreversible neuronal damage.